This application is based on Japanese Patent Application No. 2002-171536 filed on Jun. 12, 2002, the disclosure of which is incorporated herein by reference.
The present invention relates to a refrigerant cycle system having a hot gas heating function using an interior heat exchanger (evaporator) as a radiator by directly introducing a gas refrigerant (hot gas) discharged from a compressor into the interior heat exchanger. More particularly, the present invention relates to a refrigerant cycle system in which a refrigerant shortage or a refrigerant leakage in a hot-gas heating mode can be accurately determined. The system is suitably used for a vehicle air conditioner.
In a conventional vehicle air conditioner, hot water (i.e., engine cooling water) is circulated in a heating heat exchanger during a heating operation in winter to heat air by using the hot water as a heat source. In this case, when the hot water temperature is low, the temperature of air to be blown into a passenger compartment is lowered and thus may be insufficient for a heating capacity.
U.S. Pat. No. 6,266,965 (corresponding to JP-A 2001-12830) proposes a refrigerant cycle system which has a heating function by using a hot gas heater cycle. When the hot water temperature is lower than a predetermined value as just after the start-up of an engine, gas refrigerant (or hot gas) discharged from a compressor is introduced into an interior heat exchanger (evaporator) while bypassing a condenser, so that the heat from the gas refrigerant is released to the air in the interior heat exchanger, and an auxiliary heating function can be obtained.
Further, the system proposes a refrigerant shortage determination in a hot-gas heating mode, as shown in FIG. 8. In FIG. 8, a refrigerant shortage area S is determined based on the relationship between outside air temperature Tam and a high-pressure side refrigerant pressure Phi. That is, a boundary line PO between the refrigerant shortage area S and a normal area is determined in accordance with the outside air temperature Tam, and the refrigerant shortage is determined when the high-pressure side refrigerant pressure Phi is lower than the boundary line PO. However, in the refrigerant shortage determination of FIG. 8, because the refrigerant shortage is determined based on the high-pressure side refrigerant pressure Phi, the refrigerant shortage cannot be determined until a predetermined time (e.g., 30-60 seconds) passes after the hot-gas heating mode starts. Therefore, even when the refrigerant shortage is caused in the time period after the start of the hot-gas heating mode, a compressor is operated, and the life of the compressor may be reduced.
Further, in an another example of this system, refrigerant shortage is determined based on FIG. 9. In FIG. 9, line Ls indicates a saturation line of refrigerant R134, and Pat indicates the atmosphere pressure. When the saturation refrigerant pressure relative to outside air temperature Tam is higher than the atmosphere pressure Pat, the area A is the refrigerant shortage area. On the other hand, when the saturation refrigerant pressure relative to outside air temperature Tam is lower than the atmosphere pressure Pat, the area B is the refrigerant shortage area. However, as shown in FIG. 9, the refrigerant saturation pressure becomes approximately equal to the atmosphere pressure Pat in a low temperature range of xe2x88x9220xc2x0 C.-xe2x88x9230xc2x0 C., and it is difficult to determine the refrigerant shortage in the low temperature range.
In view of the above-described problems, it is an object of the present invention to provide a refrigerant cycle system which can accurately determine a refrigerant shortage during a hot-gas heating mode, in a short time after a start of operation of a compressor.
According to the present invention, a refrigerant cycle system includes a compressor for compressing refrigerant, an exterior heat exchanger disposed outside a compartment, an interior heat exchanger disposed inside the compartment, a first decompression device that decompresses refrigerant in a cooling mode for cooling the compartment by air passing through the interior heat exchanger, and a second decompression device that decompresses refrigerant in a heating mode for heating the compartment by air passing through the interior heat exchanger. The second decompression device is disposed in a hot gas bypass passage through which refrigerant discharged from the compressor is directly introduced into the interior heat exchanger while bypassing the exterior heat exchanger. In the refrigerant cycle system, a switching device is disposed for switching a cooling refrigerant cycle where refrigerant discharged from the compressor is returned to the compressor through the exterior heat exchanger, the first decompression device and the interior heat exchanger so that the cooling mode is set, and a hot gas heater cycle where the refrigerant discharged from the compressor is directly introduced to the interior heat exchanger through the hot gas bypass passage so that the hot-gas heating mode is set. Further, a control unit for controlling operation of the compressor includes: calculation means for calculating a pressure difference between a pressure of a high-pressure refrigerant in the hot gas heater cycle before being decompressed at a start time of the hot-gas heating mode, and a pressure of the high-pressure refrigerant at a predetermined time after the start of the hot-gas heating mode; and determining means for determining whether a refrigerant amount in the hot gas heater cycle is in a normal state or a shortage state. The determining means determines the normal state of the refrigerant amount when the pressure difference is within a predetermined range, and determines the shortage state of the refrigerant amount when the pressure difference is outside the predetermined range. Generally, the predetermined time after the start of the hot-gas heating mode is a short time (e.g., 5 seconds). Therefore, the refrigerant shortage state can be accurately determined for a short time after the start of the compressor.
Preferably, the predetermined range has an upper limit value and a lower limit value. Further, the determining means determines the shortage state of the refrigerant amount when the pressure difference is larger than the upper limit value or lower than the lower limit value, when temperature of outside air is equal to or lower than a predetermined outside temperature. Therefore, even when the temperature of outside air is at a low temperature lower than xe2x88x9210xc2x0 C., the refrigerant shortage can be accurately determined.
The control unit stops the operation of the compressor when the determining means determines the shortage state of the refrigerant amount. Therefore, it can prevent the compressor continuously operates for a long time in a shortage state of lubricating oil due to the refrigerant shortage, and the life of the compressor can be improved. Preferably, the predetermined range is corrected by a rotation speed of the compressor. Therefore, the refrigerant shortage can be more accurately determined.
When the refrigerant cycle system is used for a vehicle air conditioner, the compressor is driven by an engine of the vehicle. In this case, when the determining means determines the normal state of the refrigerant amount, the control unit maintains a determination output of the normal state of the refrigerant amount until information relative to temperature of the engine becomes a state corresponding to a temperature equal to or lower than a predetermined temperature. Therefore, it can prevent the shortage state of the refrigerant amount from being incorrectly determined by a temperature increase of an engine room due to heat radiation from the engine. Alternatively, the control unit starts the hot-gas heating mode to be operatively linked with a start operation of the engine, and the determining means determines the normal state or the shortage state of the refrigerant amount in the hot gas heater cycle. Even in this case, it can prevent the shortage state of the refrigerant amount from being incorrectly determined by a temperature increase of the engine room due to heat radiation from the engine.